AE ENHANCERS

// Destabilize Layer V1.0
// created by Paul Tuersley, May 2004

// This script takes a stabilized layer, precomposes it, then adds expressions
// that counter the effects of the original stabilization.

// If you are trying to Motion Track an element on to some moving footage, it is
// often easier to stabilize that footage first. You can then easily line up the
// 'element to be tracked on' over the stabilized footage before applying the
// inverse of that stabilization to reintroduce the footage's original motion.

// Here's how you do it:
// 1. Drop your movie footage into a comp and choose Animation > Stabilize Motion
// from the main menu.

// 2. Stabilize the footage. You can choose to stabilize Position, Rotation and
// Scale. When finished, hit Apply in the Tracker Controls and check the results
// of the stabilization.

// 3. With the stabilized layer selected, run the DestabilizeLayer script. You
// will now have two comps, one ending with (stab) and one with (destab).

// 4. Open the (stab) comp and place a still element or solid over the stabilized
// area.

// 5. Finally, in the (destab) comp, you will see this element is now perfectly
// (hopefully) tracked on to the movie footage.   


// main script

//  MAKE SURE COMP IS SELECTED
var activeItem = app.project.activeItem;
if (activeItem == null || !(activeItem instanceof CompItem)){
   alert("Please select the layer to destabilize and run the script again");
} else {

   // MAKE SURE 1 LAYER IS SELECTED
   var selectedLayers = activeItem.selectedLayers;
   if (activeItem.selectedLayers.length != 1 ) {
      alert("Please select one layer in the active comp and run the script again.");
   } else {
      
      app.beginUndoGroup("Destabilize Layer");

      // MAKE INDEX ARRAY FOR SELECTED LAYER FOR PRECOMPOSE
      var selectedLayerIndex = new Array();
      selectedLayerIndex[0] = selectedLayers[0].index;

      // MAKE NOTE OF STABILIZED LAYERS NAME
      var stabLayerName = selectedLayers[0].name.toString();

      // ADDS STAB TO END OF PRECOMP NAME
      // checks whether comp name is too long to add to, if so then truncates first.
      var new_name = activeItem.name;
      if (new_name.length <= 22) {
         new_name += "  (stab)";
      } else {
         new_name = new_name.substring(0,22) + "  (stab)";
      }

      // PRECOMPOSES THE STABILIZED LAYER
      activeItem.layers.precompose(selectedLayerIndex, new_name);

      // ADDS DESTAB TO END OF PRECOMP'S NAME
      // CHECKS WHETHER COMP NAME IS TOO LONG TO ADD TO, IF SO THEN TRUNCATES FIRST
      if (activeItem.name.length <= 22) {
         activeItem.name += " (destab)";
      } else {
         activeItem.name = activeItem.name.substring(0,22) + " (destab)";
      }

      // COLLAPSE TRANSFORMATIONS ON PRECOMP LAYER
      activeItem.selectedLayers[0].collapseTransformation = true;

      // SHORTCUT FOR LAYER TO DESTABILIZE
      var destab = activeItem.selectedLayers[0];

      // POSITION TO ANCHOR POINT 
      var exprString = "comp(\"" + new_name + "\").layer(\"" + stabLayerName + "\").position;";
      destab.property("Anchor Point").expression = exprString;

      // ANCHOR POINT TO POSITION
      var exprString = "comp(\"" + new_name + "\").layer(\"" + stabLayerName + "\").anchorPoint;";
      destab.property("Position").expression = exprString;

      //INVERT SCALE
      var exprString = "x = (100 / comp(\"" + new_name + "\").layer(\"" + stabLayerName + "\").scale[0]) * 100;"+
         " y = (100 / comp(\"" + new_name + "\").layer(\"" + stabLayerName + "\").scale[1]) * 100;"+
         " [x,y];";
      destab.property("Scale").expression = exprString;

      // INVERT ROTATION
      var exprString = "comp(\"" + new_name + "\").layer(\"" + stabLayerName + "\").rotation * -1;";
      destab.property("rotation").expression = exprString;   

      app.endUndoGroup();   
   }
}